1. Field of the Invention
This invention relates to a process for separating alkanols from aqueous calcium chloride. More particularly, it relates to a process for back extracting alkanols from aqueous solutions of calcium chloride-alkanol complexes formed in separating alkanols from alkyl t-alkyl ethers.
2. Description of the Prior Art
As shown in Netherlands published application No. 7,807,035 (Snam Progetti); U.S. Pat. Nos. 3,940,450 (Lee) and 4,148,695 (Lee et al.); John C. Davis et al., "MTBE bandwagon," CHEMICAL ENGINEERING, May 21, 1979, pp. 91-93; and Stephen C. Stinson, "New plants, processes set for octane booster," CHEMICAL & ENGINEERING NEWS, June 25, 1979, pp. 35 and 36, it is known that alkyl t-alkyl ethers can be prepared by reacting an isoolefin with an alkanol in the presence of an ion exchange resin. Such reactions have general interest, although the greatest current interest is in the reaction of isobutylene with methanol to form methyl t-butyl ether. Methyl t-butyl ether has utility as an additive for improving the octane rating of gasoline.
In the reactions of isoolefins with alkanols, it is preferred to use an excess of alkanol in order to minimize the formation of by-products. However, the use of an excess of alkanol results in contaminating the ether product with a difficultly removable impurity. The alkanol forms an azeotrope with the ether and therefore cannot be separated therefrom by simple atmospheric distillation.
It is frequently desirable to separate the alkanol from the ether. It is also desirable to separate the alkanol from any unreacted hydrocarbons in the crude reaction product, since alkanols are poisons for alkylation catalysts and, if not removed, would make the unreacted hydrocarbons unsuitable for use in alkylation units. Thus, since atmospheric distillation canot be used, it is conventional to remove the alkanol by pressure distillation. This method of removing the alkanol is costly in terms of energy requirements and capital investment.
An economical and efficient process for separating alkanols from alkyl t-alkyl ethers and unreacted hydrocarbons is disclosed in copending application Ser. No. 069,210, filed Aug. 23, 1979, in the names of Anderson O. Dotson, Jr., and Francis T. Wadsworth. In the preferred process of that application, aqueous calcium chloride is intimately admixed with an ether-alkanol mixture to form a calcium chloride-alkanol complex which is easily separable from the ether; and, when it is desired to reuse the calcium chloride and alkanol, the complex is separated into reusable components by stripping the alkanol at about 100.degree. C. This process has decided advantages over conventional methods of separating alkanols from ethers, but it would be desirable to find an even more economical way of separating the alkanol from aqueous calcium chloride when reuse of the alkanol and calcium chloride components of the complex is wanted.